1. Field of the Invention
The present invention relates to a fiber optic device in which an idler lightwave having a wavelength that is different from the wavelength of input signal lightwave is generated using an optical fiber.
2. Description of the Background Art
A fiber-based optical signal processing device which uses a nonlinear phenomenon that occurs in an optical fiber is known in the art. Particularly, a device that performs wavelength conversion using the four-wave mixing (FWM) that occurs in an optical fiber is widely used for processing a high-speed signal, because not only can it be used in a broad wavelength range, but also its conversion efficiency is high (e.g., see Japanese Patent Application Publication No. 2007-72182).
In this fiber optic device, in order to output an idler lightwave with an optional wavelength from a signal lightwave having an arbitrary wavelength that has been input into the fiber optical device, it is necessary to change the wavelength of a pump lightwave, corresponding to the wavelength of the input signal lightwave and that of the idler lightwave. Also, it is necessary to reduce the absolute value of the second order dispersion at the pump wavelength as much as possible. Therefore, studies have been made with respect to the wavelength conversion using a dispersion-flattened fiber which exhibits less variation in the second order dispersion value in a wide wavelength range corresponding to the pump wavelength (For example, refer to Non-patent documents 1 to 5).
The productivity of the dispersion-flattened fibers as used in Non-patent documents 1 to 5 is poor because the dispersion value changes according to minimal variation in the core diameter. Also, the nonlinear coefficient is smaller as compared with a generally used highly non-linear fiber. As for photonic crystal fibers (PCF) used for Non-patent documents 4 and 5, it is difficult to control the diameter and the position of their through-holes, and therefore it is difficult to control the second order dispersion value, which would pose a problem in practical applications.